Geochemistry of Icy-World Interiors

Shelby Gunnells

NDSU Geochemistry 2018

Intro

❖ Fluid-rock interaction in icy moons and dwarf planets➢ Product of internal heating

❖ Present day ratio of these materials, probable they were beginning materials

Ceres. WikipediaEnceladus. NASA

Purpose

❖ Interaction between fluid and rock

❖ Alterations to fluid and rock

❖ Indications of habitability to life forms➢ Oxidation of minerals provides food source for organisms

deepoceanfacts.com

Why I chose this topic

❖ Planetary studies have fascinated me

❖ Inspiration from GSA

❖ Little previous experience

Source of Data

1. PHREEQc modeling using core.dat (Castillo-Rogez et al., 2017)

2 . Specific asteroid/chondrite composition (Agee et al., 2018)

Previous Work (Castillo-Rogez et al., 2017)

❖ Took mineralogical concentrations of

average chondrite➢ Equilibrate with pure water and cometary

fluid

❖ Variables: water/rock ratios,

temperature, pressure, pe

Previous Work (Agee et al., 2018)

❖ Samples are a chondrite known as Grove Mountains (GRV) 020043➢ Part of parent asteroid

➢ Derived from protoplanetary disk or differentiated body

❖ Collected in Grove Mountains, Antarctica

Locality of sample. sciencedirect.com

Method of Modeling

❖ Ran core.dat on asteroid composition ➢ Based upon proportions for 1 mole of rock material

➢ Pure water and cometary fluid

■ Cometary fluid: 5 mol% C, 2 mol% N, 0.5 mol% S, and 520 ppm by mass Cl

➢ Baseline: 0.01ºC, 0.01 atm, 10 kg of fluid

❖ Looked for changes in the fluid and rock ➢ Changes in pH

➢ Ionic strength comparisons (compare to earth systems as well)

➢ Distribution of species

Results - Pure Water

❖ Ionic Strength: synonymous with rivers and lakes (Faure, 1998)

❖ Distribution of Species➢ Cations and metals are free ions or bonding almost specifically with O, OH, or H

*Note: Due to proportionary rock composition of 1 mole, all minerals undersaturated and with relatively low molality

Results - Cometary Fluid

❖ Ionic Strength: Synonymous with seawater (Faure, 1998)

❖ Much more neutral solution

❖ Much more variation is distribution species➢ Notably those present in fluid: C, S, N, and Cl

Comparison

❖ Other notables:➢ More speciation, but less Fe in CF

➢ Similar Na

➢ Same compounds of Si, but difference

ordering of which phase is more

abundant

■ Greater molality in pure water

Pure Water After Equilibration

Cometary Fluid After Equilibration

Conclusions

❖ Pure water was very basic➢ Few species in solution

❖ Cometary fluid equilibrated with a more diverse solution➢ Greater number of species

➢ Basic solution, but more neutral than pure water

➢ More to react with in initial solution

❖ Interaction of rock with cometary fluid leads to more alteration in icy world

setting

References

Agee, C., Bao, H., Irving, A., Li, S., Li, X., Li, Y., Marti, K., Miao, B., Sanborn, M.E., Wang, S., Yin, Q., and Ziegler, K., 2018.

Evidence for a multilayered internal structure of the chondritic acapulcoite-lodranite parent asteroid: Geochimica et

Cosmochimica Acta, v. 242, p. 82-101.

Castillo-Rogez, J.C., Desch, S.J., and Neveu, M., 2017. Aqueous geochemistry in icy world interiors: Equilibrium fluid, rock,

and gas compositions, and fate of antifreezes and radionuclides: Geochimica et Cosmochimica Acta, v. 212, p.

324-371.

Faure, G., 1998, Principles and applications of geochemistry: a comprehensive textbook for geology students: New

Jersey, Prentice Hall, Inc., 140 p.

Questions?